Coating process and apparatus



NOV; 10, 1970 M. N555 3,539,489

COATING PROCESS AND APPARATUS Filed March 13, 1967 f/l/izvzv/a Mam/v Mew 11 565 wgggg h United States Patent 3,539,489 COATING PROCESS AND APPARATUS Norman Morin Ness, Taplow, England, assignor to Imperial Chemical Industries Limited, Millbank, London, England, a corporation of Great Britain Filed Mar. 13, 1967, Ser. No. 622,764 Claims priority, application Great Britain, Mar. 16, 1966, 11,505/ 66 Int. Cl. B01k 5/02; C23]: 13/00 U.S. Cl. 204-181 Claims ABSTRACT OF THE DISCLOSURE A process for electrodepositing a coating on an electrically conductive article which is supported on a belt-like member extended in a liquid coating composition in which electric current is passed between the article and another electrode connected with one pole of the source of electric current, the belt-like member being adapted to connect the article with the other pole, and apparatus therefor.

BACKGROUND OF THE INVENTION This invention relates to a process and apparatus for electrodepositing a coating on an electrically conductive article from a liquid coating composition.

In a typical electrodeposition process an electrically conductive article is immersed in a liquid coating composition which contains a dissolved and/ or a dispersed coating material, for example a film-forming resin, and an electric current is passed between the article and another electrode to deposit on the article a layer of the coating material. The coated article may then be washed and dried and if necessary the coating cured, for example by stoving.

It is a common practice in such a process to suspend the article to be coated from an electrically conductive member which is in electrical contact with the article, the member being capable of connection with one pole of a source of electric current, and to immerse the suspended article in the coating composition while an electric current is passed between the article and another electrode connected to the other pole of the source of electric current.

This practice is particularly convenient for large articles, for example vehicle bodies, and for other articles which can be suspended from an electrically conductive member. The suspending electrically conductive member may then be, for example, a spindle which passes into or right through an open section of the article or alternatively it may comprise a hook or other means to engage securely with any suitable part of the article.

Certain aritcles, however, due for example to their shape or size, cannot be satisfactorily coated by electrodeposition in this manner since, for example, they may not have a suitable location for a suspening member or the articles may be so small that the provision of individual suspending members is impossible or uneconomic.

SUMMARY According to the present invention we provide a process of electrodepositing a coating on an electrically conductive article which comprises passing an electric current through a liquid coating composition between the article to be coated and another electrode, the article being supported upon a belt-like member extended in the composition which member is adapted to electrically connect the article with one pole of the source of electric current.

The invention also provides an apparatus for electrodepositioning a coating on an electrically conductive article which comprises a coating bath for containing a liquid coating composition, a belt-like member extended in the Patented Nov. 10, 1970 DESCRIPTION OF THE PREFERRED EMBODIMENTS It is one function of the belt-like member to support the article in the coating composition in a position suitable to receive an electro-deposited coating. When the member supports a plurality of such articles, the articles may be arranged or deposited in ordered or random manner upon the supporting member as desired. Preferably the articles are so spaced that contact between them is reduced to a minimum in order to obtain an even coating, but in some cases electrical contact between the articles may be advantageous.

The belt-like member may remain stationary during the coating process but preferably it moves continuously or intermittently through the coating composition and is thus preferably engaged with means to enable such movement. Such means include for example take-up rollers placed at each end of the travel of the belt-like member and by suitable rotation of these rollers the direction and rate of travel of the member through the composition may be varied. Preferably the member is endless so that it can be continuously recirculated through the coating composition. The belt-like member is preferably equipped with upwardly directed projections or hooks or other means which provide or assist physical contact or engagement between the article and the member.

It is another function of the belt-like member to enable electrical connection of the article to be made with one pole of the source of electric current which is employed to effect the electrodeposiiton of a coating on the article. The member will normally contain electrically conductive elements but it may be advantageous that the member is not electrically conductive throughout its entire length and/or that it is enabled to electrically connect an article with one pole of the source of electric current over only a selected length of its travel through the coating bath. However, there should be provided in the member at least one point for electrical contact between the member and the article, to which point the current is conducted.

The member may also co-operate with another belt-like member whereby for example elements to support the article and to electrically connect it to one pole of the source of electric current may project through that other member.

Thus, for example, an article to be coated may be transported by one or more additional belt-like members to and from the first belt-like member which is adapted to electrically connect the article with a pole of the source of electric current, the first belt-like member being located in the coating composition. For example, when a second belt-like member conveys an article into and out of the coating composition this second member may co-operate with the first member such that article-sup porting elements on the first member project through the second member.

The belt-like member may comprise predominantly electrically conductive material, e.g. metal mesh, or net. Preferably it has upstanding projections to support the article and provide an electrical contact between the article and the belt. Alternatively the belt-like member may comprise largely non-conductive material but with suitably spaced electrically conductive elements carried on or partially embedded in it which can make electrical contact with an article. Again these elements may have upstanding projections to support the article and to provide electrical contact.

Electrical contact between the article on the belt-like member and one pole of the source of electric current may be effected through conductive elements and by way of, for example, the means such as rollers by which the member is extended in the coating composition. Alternatively electrical contact may be maintained with one pole of the source of electric current by brush contact with electrically conductive elements on that face carrying the articles preferably through an upstanding part of the member or conductive element thereof.

The belt-like member may be of any suitable material or materials suflrciently robust and substantially chemically inert to the coating composition or alternatively which will not adversely effect the coating process.

During the electrodeposition process those electrically conductive parts of the belt-like member which are capa'ble of electrical connection With an article may become coated with coating material and thus be ineffective in electrically connecting with an article after one or more passages of the member through the coating composition. It is therefore preferred to periodically remove the electrodeposited coating from such parts of the member. This operation may conveniently be performed after each passage of the member through the coating composition. Suitable means for removing coating from such parts may be chemical or physical, for example by solvent, by wiping, brushing or abrasive action.

When the belt-like member is arranged to travel into and then out of the coating composition the amount of material removed is comparatively small. The preferred aqueous coating composition used in the electrodeposition process is of low viscosity and of low solids content and by suitable arrangement of the belt-like member a substantial proportion of the adhering material may be drained back into the bulk of the coating medium. After the electrodeposition of a coating on the article, the article may be washed to remove surplus coating composition and if necessary dried Whilst still supported on the belt-like member. Such a washing treatment may also be advantageous in cleaning the belt-like member. The washed article may be subsequently stoved where this is necessary.

The liquid coating composition is preferably an aqueous coating composition. Preferably the aqueous coating composition contains an organic film-forming material as the coating material. Suitable organic film-forming materials include the alkyd resins, epoxy resins, maleinised oils and acrylic resins used alone or in mixtures, optionally together with organic solvents and other coating additives such as pigments. When the film-forming material contains free acid groups e.g. carboxyl groups, it may be suitable when used in conjunction with a suitable base, e.g. an amine or a metal hydroxide, for anodic deposition. When the film-forming material contains basic groups e.g. amine groups, it may be suitable when used in conjunction with a suitable acid for cathodic deposition. The film-forming materials may be present in the coating composition as a solution, colloid, fine particle size dispersion and/ or emulsion.

DESCRIPTION OF THE DRAWINGS Two embodiments of an apparatus suitable for carrying out the present process are described in the accompanying drawings wherein FIG. 1 is a sectional view of an apparatus wherein one belt-like member adapted to electrically connect an article with one pole of a source of electric current conveys the article into, through, and then out of the coating composition, and FIG. 2 is a sectional view of an apparatus wherein a belt-like member adapted to electrically connect an article with one pole of a source of electric current is in contact with the article only during its passage through the coating composition.

In FIG. 1 an endless belt 5 of flexible metal mesh having outwardly directed metal spikes 9 to make electrical contact with an article 1 when placed on the belt is arranged to pass in an approximately horizontal position through a bath 8 of coating composition 2, the belt being supported on rotatable rollers 6 and 7 before it enters and after it leaves the bath. The belt is also guided and supported by guide members 3 and 4. At least one rotatable roller 6 is in electrical contact with one pole of a source of electric current and the other pole of that source is in electrical contact with the coating composition through an electrode in contact with the composition, which may be, for example, the electrically conductive wall of the bath 8. The aforesaid rotating roller is in electrical contact with the metal mesh belt and with the outwardly directed metal spikes. A brush (not shown) is suitably situated to remove an electrodeposited coating from the metal spikes of the mesh belt, after it has passed through the coating composition. Means (not shown) for washing the belt and an article thereon are provided after drainage of excess material adhering to the belt and the article has taken place.

To carry out the process an article 1 is placed on the belt 5 in electrical contact with at least one of the upwardly directed metal spikes 9 and whilst the article is immersed in the coating composition 2 an electric current is passed between the belt (and thus through the article) and the other electrode 8. The coated article is conveyed from the coating composition by movement of the belt and excess coating material adhering to the article and the belt is allowed to drain off. A brush for removing coating from the article-contacting parts of the belt is continuously operated and a washing stage frees the belt from loose coating and the article from the adhering coating composition.

The article may be subsequently dried and/ or stoved.

In FIG. 2 an endless belt 5 of flexible metal mesh provided with outwardly projecting metal spikes 10 is adapted to rotate within a bath 8 of coating composition 2 around two rotatable rollers 6 and 7 placed in the same horizontal plane. At least one roller 6 is in electrical contact with one pole of a source of electric current and with the spikes, and the other pole is in electrical contact with the coating composition through an electrode, in this case the electrically conductive wall of the bath 8 which is in contact with the composition. A non-conductive belt 9 is arranged by means of external rollers to enter the coating composition, to pass over the upper part of the endless belt so that the spikes project upwards through apertures provided in the non-conductive belt, and then to leave the coating composition.

In coating an article 1 with this apparatus the article is conveyed into the coating composition 2 on the nonconductive belt 9 until it becomes immersed in the compostion and supported on the spikes 10 of the endless belt 5. The article is coated by electrodeposition only whilst in electrical contact with the spikes and may then be conveyed from the composition by the non-conductive belt.

It is an advantage of the apparatus of FIG. 2 that an article may be conveyed directly from any pre-treatment stage to the coating bath and then to a post-treatment such as washing and stoving on a continuous length of belt. The non-conductive belt may be stoved without affecting the efiiciency of the coating process while the coating deposited on the spikes may be readily removed, for example, by brush action.

I claim:

1. In a process of electrodepositing a coating of organic film-forming material on electrically conductive articles which comprises passing an electric current through an aqueous liquid between said articles and an electrode which is in contact with said liquid and with one pole of a source of electric current, said liquid containing a film-forming material which has acid or base groups and a liquid also containing an acid when the film-forming material contains base groups and a base when said film-forming material contains acid groups; the improvement which comprises supporting said articles on an electrically non-conductive belt having a plurality of openings therethrough, introducing said belt and the supported articles into said liquid, inserting through said openings electrically conductive members which contact said articles while in said liquid, the electrically conductive members being in electrical contact with the other pole of said source of electric current, whereby said film. forming material is deposited on said articles, and removing the electrically conductive members from said openmgs.

2. Apparatus for electrodeposition of a coating of organic film-forming material on electrically conductive articles comprising a receptacle for an aqueous liquid containing said film-forming material, a first electrode mounted to contact the liquid in said receptacle and in electrical contact with one pole of a source of electric current, a non-conductive belt having openings therethrough for supporting said articles, means for introducing said belt into said receptacle and for withdrawing said belt from said receptacle, electrically conductive members in electric contact with the other pole of said source of electric current and means for inserting said electrically conductive members through said openings to contact said articles and for withdrawing them from said openings.

3. Apparatus as set forth in claim 2 in which said belt is an endless belt.

4. Apparatus as set forth in claim 2 in which said means for inserting and withdrawing said electrically conductive members is a second belt from which the electrically conductive members project, the second belt moving along a path, a part of which is parallel and adjacent to the non-conductive belt so that said electrically conductive members are inserted into said openings during that part of said path.

References Cited UNITED STATES PATENTS 799,402 9/1905 Potthoff 204202 1,168,281 6/1913 Buch 204202 1,208,584 12/1916 Laughlin 204-202 1,243,098 10/1917 Potthoif 204-202 1,336,052 4/1920 Pinger 204 202 1,950,096 3/1934 Yeager 204-202 2,011,328 8/ 1935 Tuttle 204202 2,878,171 3/ 1959 Ferrand 204202 2,887,447 5/1959 Lancy 204-297 3,254,004 5/ 1966 Jackson et al 204-181 HOWARD S. WILLIAMS, Primary Examiner N. A. KAPLAN, Assistant Examiner U.S. Cl. X.R. 204300 

